Method for marking or cutting a material along predetermined paths

ABSTRACT

Each path (P 1  -P 10 ) is travelled by moving a tool in two directions in a determined working zone (20) through which the material (22) is advanced intermittently under the action of a control circuit that is separate from the control circuit of the tool, without the work of the tool being totally interrupted while the material is advancing. Each time the material advances, it does so over a distance that is less than the length of the working zone, as measured in the advance direction of the material, and while the material is advancing, the tool is caused to travel along at least a portion of one or more paths (P 6  -P 8 ) over a portion of the material that is already within the working zone prior to the advance, and that is not removed from the working zone during the advance.

The present invention relates to a method of performing plotting orcutting along predetermined paths on a material.

The invention is particularly applicable to plotters and engraving orcutting machines in which plotting or cutting corresponding topredetermined drawings is performed on a material by means of relativedisplacement between the material and a tool, such as a writing,engraving, or cutting tool.

The invention relates more precisely to machines that include a workingzone or table on which plotting, engraving or cutting is performed bydisplacing the tool relative to the material in two directions withinthe working zone successive portions of the material being fed into theworking zone under the action of a control circuit that is separate fromthe control circuit of the tool.

This applies in particular to numerically-controlled cutting machinesused for cutting fabrics, felts, leathers, or other flexible sheetmaterials in the clothing industry, the furniture industry, etc. In suchmachines, cutting may be performed for example by means of a vibratingblade, a cutting wheel, a laser beam, or a water jet under pressurecarried by a cutting head which is displaced relative to the materialwithin the working zone in two different directions. The material may bedisposed in superimposed layers forming a lay-up so that cutting can beperformed through a plurality of layers simultaneously.

The pieces are cut out following a predetermined layout which is definedso as to minimize wasted material. In order to limit the size of themachines, the working zone in which cutting is performed may have alength that is less than that of an entire layout while having a widththat is equal to that of the material.

In order to cut out all of the pieces in a layout, it is thereforenecessary to cause the sheet material to advance intermittently so as tobring new portions of the material into the working zone, with materialadvance being controlled separately from cutting head displacement.

The same applies to numerically-controlled plotters that print on acontinuous material (paper or some other sheet material) and thatinclude a table XY on which plotting is performed by displacing awriting tool in two different directions, which are often orthogonal,the table having a length, in the longitudinal direction of thecontinuous material, that is shorter than the length taken up by adrawing or a set of drawings to be reproduced.

In such known machines, the material is caused to advance after all ofthe required plotting or cutting-out has been performed on that portionof the material which is situated in the working zone, the tool being inthe rest position during material advance. The material is caused toadvance over a length substantially corresponding to the length of theworking zone, so as to bring a new portion of the material into theworking zone.

A drawback with such prior art machines is that productivity is lost dueto the plotting or cutting-out operations being interrupted while thematerial advances.

In order to reduce such loss of productivity, it is possible to causethe material to advance as quickly as possible. However, this subjectsthe material to stresses, and with thin and flexible materials, suchstresses can cause the material to slip or cause creases to formtherein, thereby reducing the accuracy of plotting or cutting-out.Furthermore, since each time the material advances, it does so over thelength of the working zone, it is necessary to provide an unloading zonethat is of at least the same length, which poses problems of cost, ofcompactness, and of accessibility;

Suggestions have been made in principle to avoid loss of productivity bynot interrupting the work of the tool during material advance. To thisend, reference can be made to Document FR-A-2 640 202.

However, the working region of the tool is then limited to the newportions of material that are progressively brought into the workingzone during advance, and the velocity component of the tool in thelongitudinal direction opposite to the advance direction cannot begreater than speed of advance. Unfortunately, as indicated above, thespeed of advance cannot be very high. Moreover, any plotting andcutting-out that is not completed because it does not lie entirelywithin the working zone must be interrupted and then resumed. A veryhigh degree of accuracy is then necessary to ensure that the plottingand cutting-out is resumed without any offset whatsoever when highquality plotting is desired, or so as to guarantee cutting continuity.Achieving such accuracy poses practical problems, in particular withnon-rigid materials.

An object of the present invention is to provide a method which avoidsany loss of productivity due to interrupting the work of the tool whilethe material is advancing, but which does not suffer from theabove-mentioned drawbacks.

This object is achieved by the fact that, according to the invention,each time the material advances it does so over a distance that is lessthan the length of the working zone, as measured in the advancedirection of the material, and the tool is controlled while the materialis advancing so as to travel along at least a portion of one or morepaths over a portion of the material that is already within the workingzone prior to the advance, and that is not removed from the working zoneduring the advance.

By means of this disposition, no restriction is imposed on the toolwhile the material is advancing. Thus, tool control need not differdepending on whether the material is stationary or advancing, providedthat during material advance, the co-ordinate of the tool relative tothe material in the advance direction is continuously corrected bycalculation so as to take the displacement of the material into account.Thus, no time is wasted while the material is advancing because thematerial is advanced completely while plotting or cutting-out is beingformed.

In an implementation of the method of the invention, a working window isdefined having a predetermined length in the advance direction of thematerial, which length is less than the length of the working zone, and,after at least a portion of the paths lying within the window has beentravelled, the working window is shifted towards the upstream end of theworking zone so as to take up a position in which it covers at leasteach path or path portion that has not yet been travelled and that issituated further downstream, and the material is caused to advance whilethe working window is simultaneously displaced.

Thus, in this implementation, a floating working window is defined whichhas a length less than the length of the working zone, and inside whichthe work of the tool is confined.

For example, a working window may be chosen having a length equal tohalf the length of the working zone. In which case, with the workingwindow occupying the downstream half of the working zone, all of thepaths situated within the window are travelled. The working window isthen shifted upstream, e.g. over its entire length, so as to occupy theupstream half of the working zone, and the material is caused to advanceover a length equal to the length of the window. As soon as the materialstarts advancing, the tool is controlled so that it starts travellingalong the paths situated within the working window, said working windowbeing displaced simultaneously with the material so as to occupy thedownstream half of the working zone again, the tool continuing to workafter the advance has ended so as to travel along all of the pathssituated within the window.

In order to limit the number of paths along which travel is interruptedand then resumed, it is also possible to cause the upstream shift of theworking window and the simultaneous advance of the material and of theworking window to be effected over a length that is less than the lengthof the window. In this way, two successive positions of the windowoverlap. When the window is in its first position, it is thus possiblenot to start travelling in the overlap zone along portions of paths thatare situated in the upstream portion of the window, and to wait untilthe window is in its second position so as to travel withoutinterruption along these paths, thereby avoiding interruption andresumption of travel.

In another implementation of the method of the invention, each advanceof the material is determined so as to enable each path to be travelledwithout interruption from the start of one advance to the start of thefollowing advance. Naturally, it is assumed that each path fits entirelyinside the working zone. In the event that a few paths do not satisfythis prior condition, each of these paths is subdivided into a pluralityof paths, each of which does fit inside the working zone.

Each time the material advances, it does so over a length not more thana first value that is equal to the distance between the downstream endof the working zone and the closest downstream end of a location for apath that has not yet been travelled.

Preferably, each time the material advances, it then does so over alength not less than a second value that is equal to the largest of thedistances between the upstream end of the working zone and the upstreamends of the locations for paths that do not yet lie entirely within theworking zone, said second value remaining not more than said firstvalue. In this way, it is possible to ensure that the location of atleast one new path lies entirely within the working zone.

The invention will be better understood on reading the followingdescription given by way of non-limiting example and with reference tothe accompanying drawings, in which:

FIG. 1 is a very diagrammatic view of a cutting machine in which themethod of the invention can be implemented;

FIGS. 2A to 2D are views of positions taken up in a working zone of themachine shown in FIG. 1 by a working window and by a material from whichpieces are to be cut out following a predetermined layout, in a firstimplementation of the method of the invention;

FIG. 3 is a flow chart showing the various stages of the firstimplementation of the method of the invention;

FIGS. 4A to 4C show a variant of the first implementation of the methodof the invention;

FIGS. 5A to 5D are views of positions taken up in a working zone of themachine shown in FIG. 1 by a material from which pieces are to be cutout following a predetermined layout, in a second implementation of themethod of the invention; and

FIG. 6 is a flow chart showing the various stages of the secondimplementation of the method of the invention.

Two implementations of the invention are now described.

The first implementation is preferably for use in applications in whichtravel along the paths to be followed may be interrupted and thenresumed, e.g. after the material has advanced, without any particularproblems being encountered, whereas the second implementation is moresuited to applications in which it is preferable to avoid interruptionand resumption of travel along any of the paths. The firstimplementation is preferably applied to plotting operations, where theline being offset slightly when plotting is resumed does not constitutea drawback. The second implementation is preferably applied to cuttingor engraving operations, or to plotting operations in which perfectcontinuity of the line is desirable.

Both implementations are applicable to numerically controlled machinesin which the tool is driven along two axes X and Y over a working zoneof a support for advancing or facilitating the advance of the materialon which the tool is to act. The material advances in a direction thatis parallel to the plane defined by the axes X and Y, but that is notnecessarily parallel to one of the axes, with the advance of thematerial being controlled separately from the tool.

As indicated above, the operations performed on the material may be ofvarious types: plotting, partial or total cutting, scoring, orengraving, and they may use various types of tools. In mostapplications, the material is in the form of a flexible or rigid sheet,strip, or plate.

FIG. 1 shows, very diagrammatically, the general design of a machine forautomatically plotting outlines on a material, or for automaticallycutting out pieces from a material. Such a numerically controlledmachine for plotting lines on a sheet of material, or for cutting outpieces from such a material is well known, in particularly in theclothing industry.

For example, plotting or cutting is performed by means of a suitabletool 10, e.g. a felt-tip marker or a laser-beam generator carried by ahead 12. The head is displaced along two orthogonal axes X and Yrelative to a horizontal working zone 20 occupied by a sheet of material22, e.g. a fabric.

The working zone 20 is constituted by the horizontal top portion of anendless conveyor 24 on which the material 22 is conveyed from anupstream feed station, and the cut-out pieces are removed from theconveyor at a downstream unloading station. The endless conveyor 24 isdisplaced such that it causes the material to advance intermittentlyinto the working zone as the pieces are cut out from it. The material ismoved by the conveyor merely under the effect of gravity. Additionalmeans for securing the material to the conveyor may be provided, e.g.pressure wheels pressing against the longitudinal edges of the material.

The head 12 is displaced along X and Y (X being the longitudinaldirection that is parallel to the advance direction in this example) byrespective motors 32, 34 on the basis of signals supplied by a controlunit 40. The unit 40 may consist of a computer. The computer 40 controlsthe displacement of the head 12 so as to enable the tool 10 to travelalong predetermined paths, e.g., in the clothing industry, pathscorresponding to a pre-established layout in the run of fabric. For thispurpose, the computer 40 receives graphics data representing paths to betravelled from a memory or from a host computer. The position of thehead 12 is servo-controlled to each of the axes X and Y. Real positioninformation X_(R) is given by a sensor, such as an angular-positionencoder 42 mounted on the shaft of the motor 32, and it is compared bythe computer 40 with a reference value X_(C) so as to generate an errorsignal, and so as to control the motor 32. In the same way, the motor 34is controlled as a function of an error signal obtained by comparing areference value Y_(C) with real position information Y_(R) indicatingthe real position of the head 12 along the axis Y. The information Y_(R)is given by an angular-position encoder 44 mounted on the shaft of themotor 34. Furthermore, for each path, the computer 40 determines thespeed and the acceleration of the head 12. The computer 40 also controlsa motor 36 which drives the conveyor in closed-loop motion so as tocause the material 22 to advance into the working zone 20intermittently. An angular-position encoder 46 mounted on the shaft ofthe motor 36 supplies real position information A_(R) indicating thereal position of the conveyor, which information is compared with areference value A_(C) by the computer 40 so as to control the motor 36such that the conveyor advances over a predetermined distance.

A general description of a first implementation of the method of theinvention is given below with reference to FIGS. 2A to 2D and as appliedto plotting the outlines of pieces on the material 22.

In dashed lines, FIG. 2A shows the outlines of the pieces to be plottedon the material 22 and corresponding to a pre-established layout. Theworking zone 20 is, in general, much shorter than the pre-establishedlayout (which may be several meters long, or even several tens of meterslong). The machine is therefore compact, but cutting out the entirelayout requires the material 22 to be advanced intermittently.

The tool works within a working window 20A having a length l_(A), in theadvance direction of the material 22, that is less than the length L ofthe working zone 20. In the example shown, length l_(A) is equal to L/2.

Initially, the material 22 is stationary, with its leading end situatedat the downstream end of the working zone 20, and the window 20Aoccupies the downstream half of the working zone 20. The tool isdisplaced under the control of the computer so as to plot the piecessituated in the window 20A (FIG. 2B), i.e. by causing the tool to travelalong the entire set of paths situated within the window.

Once this initial stage has been performed, the window 20A is shiftedupstream so as to occupy the upstream half of the working zone 20 (theorigin of the window is positioned at the abscissa L/2), the tool isbrought into the window, and the material 22 is caused to advance (FIG.2C). During this advance, the tool is controlled by the computer so asto plot the paths situated within the window 20A which is displaceddownstream in synchronization with the material. During the advance, theposition of the tool is servo-controlled to reference values X_(C) +DAV,Y_(C), where DAV is the length remaining to be travelled by the materialuntil the end of the advance. The value DAV is deduced from theinformation output by the sensor 46 associated with the drive motor ofthe conveyor, so as to ensure that the position of the tool isservo-controlled to the position of the working window. Thus, during theadvance, plotting takes place without interruption, the onlymodification to be made relative to plotting with the conveyor stoppedconsisting in continuously adjusting the abscissa reference value of thetool.

At the end of the advance, cutting-out is continued and finished in thewindow 20A which has returned to the downstream half of the working zone20 (FIG. 2D).

This processes is repeated until the entire layout has been plotted. Anelementary sequence of the process is described by the algorithm shownin FIG. 3.

The various operations commanded by the computer 40 are read (stage100). If the command is a command to execute plotting, it is executed(stage 101). The same applies if the command is a command to execute anoperation other than advancing the material (phase 102), e.g. raising orlowering the writing tool.

If the command is a command to advance the material, a test is performedto check whether the preceding advance is still in progress (stage 103).If it is, the advance in progress is accelerated (stage 104), and theend of the advance is detected (stage 105).

Once the preceding advance has ended, the tool is positioned at the DAVabscissa (equal to L/2 before the start of the advance) which serves asa new origin (stage 106), i.e. the working window is displaced. Theposition of the tool is servo-controlled to the position of the conveyor(stage 107), and advance of the material is started (stage 108). Theadvance is monitored (stage 109) to detect the end thereof, and, once alength L/2 has been advanced, advance is stopped, as isservo-controlling the position of the tool to the position of theconveyor (stage 110).

Naturally, when the advance direction of the conveyor is not parallel toeither of the two displacement axes of the tool, servo-controlling theposition of the tool to that of the conveyor requires both referenceco-ordinates of the tool to be modified.

In the above description, the length of the working window is equal tohalf the length of the working zone.

In a variant, it is possible (FIG. 4A) to choose a working window 20Bhaving a length l_(B) that is different from L/2, e.g. that is greaterthan L/2.

In which case, each advance must be made over a length of not more thanL-l_(B) so that, at the start of an advance (FIG. 4B), the window 20Btakes up a position in which it overlaps its preceding position (shownin dashed lines in FIG. 4B).

Thus, in order to avoid interrupting and then resuming travel along apath, it is possible, during a particular stage of the method (i.e.between two consecutive advances), to omit plotting the path portionsthat are situated in the vicinity of the upstream end of the window inthe overlap zone 20C. For example, this applies to the path T. This pathcan then be plotted without interruption during the next stage (FIG.4C).

The first implementation described enables the material 22 to beadvanced while plotting is being performed, thereby considerablyreducing any productivity loss due to the time required for advancing.

However, when a piece does not lie entirely within the window, it cannotbe plotted in a single operation, except in the specific case mentionedwith respect to the above-described variant.

In practice, resuming travel along a path after the material has beendisplaced is difficult to achieve without any offset. Although thismight be acceptable for plotters, with cutters, any offset, howeversmall, might be unacceptable because the piece in question is not fullycut-out and needs to be finished off manually.

Another implementation of the method of the invention making it possibleto perform uninterrupted cutting-out, and therefore not suffering fromthis drawback, is described below with reference to FIGS. 5A to 5D. Itis assumed that the working zone is long enough for each piece in thelayout to fit within the zone, or, if a piece is longer than the workingzone, it is assumed that the piece has been sub-divided into a pluralityof pieces, each of which fits within the working zone.

In dashed lines, FIG. 5A shows the outlines of the pieces correspondingto the predefined layout, at the leading end of the material 22, whichend has been brought into the working zone 20.

In the second implementation, a piece is cut out only if it liesentirely within the working zone after the penultimate advance. The lastadvance must then not be too long so that the piece is not removed fromthe working zone before it has been cut out.

Once the leading end of the material has been brought to the downstreamend of the working zone, the piece(s) whose upstream ends are theclosest to the downstream end of the working zone are cut out. In theexample shown in FIG. 5B, these pieces are pieces P1 and P2.

The material can then be advanced over a length of less than InfP3, i.e.the distance, at the start of the advance, between the downstream end ofthe working zone and the closest downstream end of the location of a noncut-out piece (piece P3, in this example). Preferably, and if it ispossible, the advance is performed over a distance of not less than thedistance necessary to bring into the working zone those pieces whoselocations on the material have their upstream ends closest to thedownstream end of the working zone. In the example shown, this appliesto piece P8 only, for which this distance BP8 is less than InfP3.

During this advance, and after the end of it, the pieces P3, P4, P5whose locations were originally in the working zone, may be cut out(FIG. 5C). Naturally, during the advance, the position of the cuttinghead is servo-controlled to the position of the conveyor, as describedabove with respect to the first implementation.

A second advance may be commanded over a length that is less than thedistance InfP7 between the downstream end of the working zone and theclosest downstream end of a location of a non cut-out piece (piece P7 inthis example). This advance is performed over a length that is greaterthan the distances BP9 and BP10 between the upstream end of the workingzone and the closest upstream ends of the locations on the material ofthe pieces P9 and P10 that do not yet lie fully within the working zone,since Inf7 is greater than BP9 and BP10.

During the second advance, and after the end of it, those pieces P6 andP7 whose locations lie within the working zone after the end of thefirst advance can be cut out (FIG. 5D).

The process continues in this way until the entire layout has been cutout. An elementary sequence of this process is described by theflow-chart shown in FIG. 6.

Initially, parameters m, n, k and B are set respectively to the valuesm=1, n=1, k=0, B=0 (stage 200) and, so long as the entire layout has notbeen cut out (test 201), the set E of pieces P_(i) in the layout lyingwithin the working zone (stage 202) is determined (where i is an integerthat is not less than 1). This involves seeking that value of n forwhich, regardless of i≦n, ##EQU1## where Sup P_(i) is the abscissa, asmeasured from an origin O situated at the downstream end of the workingzone, of the upstream end of the piece P_(i) (it is assumed that piecesP₁ to P_(m-1), have already been cut out). By way of example, in FIG.5B, the abscissa Sup P₅ is shown for piece P₅.

If the set E is not empty (test 203), the minimum distance A between thedownstream end of the working zone and the closest downstream end of anon cut-out piece is calculated: ##EQU2## where Inf P_(i) is theabscissa of the downstream end of piece P_(i) (stage 204). The maximumdistance B between the upstream end of the working zone and an upstreamend of a non cut-out piece that does not yet lie entirely within theworking zone is calculated: ##EQU3## where P_(j) is the abscissa of theupstream end of piece P_(j), and N is the total number of pieces to becut out (stage 205), with the condition Sup P_(j) -L≦A (so as to preventthe following advance from causing a non cut-out piece to be removedfrom the working zone). If the value B is zero (test 206), piece P_(m)is cut out (stage 207), the value of n is incremented by unity (stage208) and test 201 is started again.

If the value B is not zero (test 206), an advance stage of lengthB_(k+1) =B is commanded, where k is the number of advances made (stage209), and piece P_(n) is cut out by going on to stage 207. During theadvance, the abscissa of the tool is servo-controlled to the position ofthe conveyor, and the values Inf P_(i) and Sup P_(i) of all of thepieces P_(i) for which m≅i≦N are corrected so that they read: ##EQU4##where B_(k) and B_(k+1) are the lengths of the k^(th) and (k+1)^(th)advances.

The above-described cutting-out method may be implemented through one ormore superposed layers of material, e.g. a plurality cf layers of fabricforming a lay-up. Automatic machines making it possible to cut outpieces from such lay-ups are well known.

It appears from the above that the method of the invention is remarkablein that it enables the tool to work while the material is advancing,thereby increasing productivity without having to make significantchanges to the control circuit of the machine in which the method isinstalled.

In particular, all of the features and safety devices available inexisting machines, whether they be plotters or cutters, may be retained,e.g. such as automatic re-starting after an incident.

I claim:
 1. A method for plotting or cutting along predetermined pathson material with a tool wherein the tool is displaced by a first controlcircuit in two directions within a predetermined working zone throughwhich the material is intermittently advanced by a second controlcircuit from an upstream end of the working zone to a downstream end ofthe working zone, wherein a working window comprises a length in thedirection of the advance of the material, which length is less than thelength of the working zone, and wherein the method comprises the stepsof:a. advancing the material for a distance that is less than the lengthof the working zone as measured in the direction of the advance of thematerial; b. controlling the tool while the material is advancing sothat the tool travels along at least a part of one or more paths locatedin a portion of the material which is in the working zone prior toadvancing the material and which remains in the working zone afteradvancing the material; c. shifting the working window toward theupstream end of the working zone, after at least a portion of the pathslying within the working window have been traveled, so that the workingwindow is positioned to cover at least each path or path portion thathas not yet been traveled within the working zone.
 2. The method ofclaim 1, wherein the advancing step further comprises advancing thematerial while the working window is shifting from the downstream end tothe upstream end of the working zone.
 3. The method of claim 2, whereinthe working window has a length equal to half the length of the workingzone.
 4. The method of claim 2, wherein the working window has a lengththat is greater than half the length of the working zone, and each timethe material advances, it does so over a distance not more than thedifference between the length of the working zone and the length of theworking window.
 5. The method of claim 1, wherein the advancing stepfurther comprises advancing the material not more than a first distancethat is equal to the distance between the downstream end of the workingzone and the closest downstream end of a location for a path that hasnot been traveled by the tool prior to advancing the material.
 6. Themethod of claim 5, wherein the advancing step further comprisesadvancing the material not less than a second distance that is equal tothe largest of the distances between the upstream end of the workingzone and the upstream ends of the locations for paths that do not yetlie entirely within the working zone, wherein the second distance is notmore than the first distance.
 7. A plotting or cutting apparatus forplotting or cutting along predetermined paths on material with a toolwherein the apparatus comprises:a. a working surface on which thematerial is disposed and including a predetermined working zone; b. afirst control circuit for co controlling the movement of the tool in twodirections within the predetermined working zone; c. a second controlcircuit for intermittently advancing the material through the workingzone from an upstream end of the working zone to a downstream end of theworking zone;wherein the second control circuit advances the materialfor a distance that is less than the length of the working zone asmeasured in the direction of the advance of the material and the firstcontrol circuit controls the travel of the tool while the material isadvancing so that the tool travels along at least a part of one or morepaths located in a portion of the material which is in the working zoneprior to advancing the material an d which remains in the working zoneafter advancing the material and wherein the first control circuitconstrains the operation of the tool to a working window having a lengthin the direction of the advance of the material, which length is lessthan the length of the working zone and wherein the working windowshifts toward the upstream end of the working zone, after at least aportion of the paths lying within the working window have been traveled,so that the working window is positioned to cover at least each path orpath portion that has not vet been traveled within the working zone. 8.The apparatus of claim 7, wherein the second control circuit advancesthe material while working window is shifting from the downstream end tothe upstream end of the working zone.
 9. The apparatus of claim 8,wherein the working window has a length equal to half the length of theworking zone.
 10. The apparatus of claim 9, wherein the working windowhas a length that is greater than half the length of the working zone,and each time the material advances, it does so over a distance not morethan the difference between the length of the working zone and thelength of the working window.
 11. The apparatus of claim 7, wherein thesecond control circuit advances the material not more than a firstdistance that is equal to the distance between the downstream end of theworking zone and the closest downstream end of a location for a paththat has not been traveled by the tool prior to advancing the material.12. The apparatus of claim 11, wherein the second control circuitadvances the material not less than a second distance that is equal tothe largest of the distances between the upstream end of the workingzone and the upstream ends of the locations for paths that do not yetlie entirely within the working zone, wherein the second distance is notmore than the first distance.